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Erramilli SK, Dominik PK, Deneka D, Tokarz P, Kim SS, Reddy BG, Skrobek BM, Dalmas O, Perozo E, Kossiakoff AA. Conformation-specific Synthetic Antibodies Discriminate Multiple Functional States of the Ion Channel CorA. J Mol Biol 2023; 435:168192. [PMID: 37394032 PMCID: PMC10529903 DOI: 10.1016/j.jmb.2023.168192] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2023] [Revised: 06/20/2023] [Accepted: 06/26/2023] [Indexed: 07/04/2023]
Abstract
CorA, the primary magnesium ion channel in prokaryotes and archaea, is a prototypical homopentameric ion channel that undergoes ion-dependent conformational transitions. CorA adopts five-fold symmetric non-conductive states in the presence of high concentrations of Mg2+, and highly asymmetric flexible states in its complete absence. However, the latter were of insufficient resolution to be thoroughly characterized. In order to gain additional insights into the relationship between asymmetry and channel activation, we exploited phage display selection strategies to generate conformation-specific synthetic antibodies (sABs) against CorA in the absence of Mg2+. Two sABs from these selections, C12 and C18, showed different degrees of Mg2+-sensitivity. Through structural, biochemical, and biophysical characterization, we found the sABs are both conformation-specific but probe different features of the channel under open-like conditions. C18 is highly specific to the Mg2+-depleted state of CorA and through negative-stain electron microscopy (ns-EM), we show sAB binding reflects the asymmetric arrangement of CorA protomers in Mg2+-depleted conditions. We used X-ray crystallography to determine a structure at 2.0 Å resolution of sAB C12 bound to the soluble N-terminal regulatory domain of CorA. The structure shows C12 is a competitive inhibitor of regulatory magnesium binding through its interaction with the divalent cation sensing site. We subsequently exploited this relationship to capture and visualize asymmetric CorA states in different [Mg2+] using ns-EM. We additionally utilized these sABs to provide insights into the energy landscape that governs the ion-dependent conformational transitions of CorA.
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Affiliation(s)
- Satchal K Erramilli
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA
| | - Pawel K Dominik
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA
| | - Dawid Deneka
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA
| | - Piotr Tokarz
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA
| | - Sangwoo S Kim
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA
| | - Bharat G Reddy
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA
| | - Blazej M Skrobek
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA; Intercollegiate Faculty of Biotechnology of University of Gdansk and Medical University of Gdansk, Gdansk, Poland
| | - Olivier Dalmas
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA
| | - Eduardo Perozo
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA; Grossman Institute for Neuroscience, Quantitative Biology and Human Behavior, The University of Chicago, Chicago, IL, USA
| | - Anthony A Kossiakoff
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA; Institute for Biophysical Dynamics, The University of Chicago, Chicago, IL, USA.
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Erramilli SK, Dominik PK, Deneka D, Tokarz P, Kim SS, Reddy BG, Skrobek BM, Dalmas O, Perozo E, Kossiakoff AA. Conformation-specific synthetic antibodies discriminate multiple functional states of the ion channel CorA. bioRxiv 2023:2023.05.07.539746. [PMID: 37205530 PMCID: PMC10187328 DOI: 10.1101/2023.05.07.539746] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
CorA, the primary magnesium ion channel in prokaryotes and archaea, is a prototypical homopentameric ion channel that undergoes ion-dependent conformational transitions. CorA adopts five-fold symmetric non-conductive states in the presence of high concentrations of Mg 2+ , and highly asymmetric flexible states in its complete absence. However, the latter were of insufficient resolution to be thoroughly characterized. In order to gain additional insights into the relationship between asymmetry and channel activation, we exploited phage display selection strategies to generate conformation-specific synthetic antibodies (sABs) against CorA in the absence of Mg 2+ . Two sABs from these selections, C12 and C18, showed different degrees of Mg 2+ -sensitivity. Through structural, biochemical, and biophysical characterization, we found the sABs are both conformation-specific but probe different features of the channel under open-like conditions. C18 is highly specific to the Mg 2+ -depleted state of CorA and through negative-stain electron microscopy (ns-EM), we show sAB binding reflects the asymmetric arrangement of CorA protomers in Mg 2+ -depleted conditions. We used X-ray crystallography to determine a structure at 2.0 Å resolution of sAB C12 bound to the soluble N-terminal regulatory domain of CorA. The structure shows C12 is a competitive inhibitor of regulatory magnesium binding through its interaction with the divalent cation sensing site. We subsequently exploited this relationship to capture and visualize asymmetric CorA states in different [Mg 2+ ] using ns-EM. We additionally utilized these sABs to provide insights into the energy landscape that governs the ion-dependent conformational transitions of CorA.
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Mukherjee S, Erramilli SK, Ammirati M, Alvarez FJD, Fennell KF, Purdy MD, Skrobek BM, Radziwon K, Coukos J, Kang Y, Dutka P, Gao X, Qiu X, Yeager M, Eric Xu H, Han S, Kossiakoff AA. Synthetic antibodies against BRIL as universal fiducial marks for single-particle cryoEM structure determination of membrane proteins. Nat Commun 2020; 11:1598. [PMID: 32221310 PMCID: PMC7101349 DOI: 10.1038/s41467-020-15363-0] [Citation(s) in RCA: 37] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2019] [Accepted: 03/03/2020] [Indexed: 12/22/2022] Open
Abstract
We propose the concept of universal fiducials based on a set of pre-made semi-synthetic antibodies (sABs) generated by customized phage display selections against the fusion protein BRIL, an engineered variant of apocytochrome b562a. These sABs can bind to BRIL fused either into the loops or termini of different GPCRs, ion channels, receptors and transporters without disrupting their structure. A crystal structure of BRIL in complex with an affinity-matured sAB (BAG2) that bound to all systems tested delineates the footprint of interaction. Negative stain and cryoEM data of several examples of BRIL-membrane protein chimera highlight the effectiveness of the sABs as universal fiducial marks. Taken together with a cryoEM structure of sAB bound human nicotinic acetylcholine receptor, this work demonstrates that these anti-BRIL sABs can greatly enhance the particle properties leading to improved cryoEM outcomes, especially for challenging membrane proteins.
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Affiliation(s)
- Somnath Mukherjee
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA
| | - Satchal K Erramilli
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA
| | - Mark Ammirati
- Medicine Design, Worldwide Research and Development, Pfizer Inc., Eastern Point Road, Groton, CT, 06340, USA
| | - Frances J D Alvarez
- Medicine Design, Worldwide Research and Development, Pfizer Inc., Eastern Point Road, Groton, CT, 06340, USA
| | - Kimberly F Fennell
- Medicine Design, Worldwide Research and Development, Pfizer Inc., Eastern Point Road, Groton, CT, 06340, USA
| | - Michael D Purdy
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, VA, USA
| | - Blazej M Skrobek
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA
- Gene Center and Department of Biochemistry, Ludwig Maximilian University of Munich, Munich, Germany
| | - Katarzyna Radziwon
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA
- Department of Biochemistry, University of Wisconsin Madison, Madison, WI, USA
| | - John Coukos
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA
| | - Yanyong Kang
- Center for Cancer and Cell Biology, Structural Biology Program, Van Andel Research Institute, Grand Rapids, MI, USA
- Takeda San Diego Inc., San Diego, CA, USA
| | - Przemysław Dutka
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, USA
| | - Xiang Gao
- Center for Cancer and Cell Biology, Structural Biology Program, Van Andel Research Institute, Grand Rapids, MI, USA
| | - Xiayang Qiu
- Medicine Design, Worldwide Research and Development, Pfizer Inc., Eastern Point Road, Groton, CT, 06340, USA
| | - Mark Yeager
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, VA, USA
| | - H Eric Xu
- Center for Cancer and Cell Biology, Structural Biology Program, Van Andel Research Institute, Grand Rapids, MI, USA
- Key Laboratory of Receptor Research, VARI-SIMM Center, Center for Structure and Function of Drug Targets, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Seungil Han
- Medicine Design, Worldwide Research and Development, Pfizer Inc., Eastern Point Road, Groton, CT, 06340, USA
| | - Anthony A Kossiakoff
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA.
- Institute for Biophysical Dynamics, University of Chicago, Chicago, IL, USA.
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